1. Field of the Invention
The present invention relates generally to an improved process for preparing certain benzyl ester insecticides. More particularly, the invention relates to a process in which an acid halide is reacted with an aldehyde and a water soluble cyanide in water and in the presence of a tetraalkyl ammonium halide wherein each alkyl group contains from 1 to about 4 carbon atoms.
2. Description of the Prior Art
Benzyl esters of the pyrethroid type having insecticidal activity have been described in the literature. See, in this regard, U.S. Pat. No. 4,024,163 issued to Elliott et. al. This patent discloses a number of synthetic esters which may be represented by the following general formula: ##STR1## wherein R represents a substituted or unsubstituted aromatic group, Y represents hydrogen or cyano, and X represents halogen.
One particularly interesting group of these materials are those in which Y in the above formula represents a cyano group. However, one problem in the processes previously available for the preparation of these cyano substituted materials is the requirement that the esterification reaction be carried out in the presence of relatively large amounts of organic solvents. As is well known, the use of such solvents introduces a number of problems into the commercialization of the process. In addition, the previously available processes often involved one or more of the following: low yields, long reaction times and low purity.
One method for preparing cyano substituted benzyl esters of the general type indicated above is disclosed in U.S. Pat. No. 3,835,176 issued to Matsuo et. al. This patent relates to alpha-cyanobenzyl cyclopropanecarboxylates and discloses that these materials may be prepared by reacting an acid halide and an aldehyde in an aqueous solution of sodium or potassium cyanide and an aprotic solvent. Specifically, this patent indicates that "a mixture of the acid chloride . . . and the aldehyde . . . or a solution of the mixture in an aprotic solvent is added to an aqueous solution of sodium or potassium cyanide, and the resulting mixture is stirred to obtain the alpha-cyanobenzyl-cyclopropanecarboxylate" (column 3, lines 49-55).
Another reference, U.S. Pat. No. 4,110,361 issued to Sheldon et. al., discloses basically the same process and adds the use of an onium catalyst to the reaction mixture. In accordance with the teachings of this patent, either a quarternary onium compound or a sulfonium compound may be employed as a catalyst in this reaction. A number of suitable onium compounds are disclosed in the reference. However, as noted above, the process requires a relatively large amount of an aprotic solvent.